An in vivo model for intraoperative assessment of impingement and dislocation in total hip arthroplasty.

We have developed an intraoperative model to quantify total hip arthroplasty impingement and dislocation mechanics using fluoroscopy and shape-matching techniques. Two patient groups were investigated: group 1 consisted of 12 hips using 28- or 32-mm femoral heads and an anterolateral surgical approach, and group 2 consisted of 17 hips using 22- or 26-mm femoral heads and a posterolateral surgical approach. During intraoperative hip stability testing consisting of extension and external rotation motions, group 1 was more unstable, and prosthetic impingement was the major reason for dislocation. With flexion and internal rotation motions, group 2 was more unstable, and superior-lateral impingement or soft tissue traction was the major reason for dislocation. Intraoperative quantitative assessment of hip mechanics provides a safe and clinically relevant method to characterize potential complications and evolve techniques to prevent them.